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Traveling between cities in the US and other countries requires conversions between Centigrade and Fahrenheit, as well as between Kilos and Pounds. Here's a easy way to do the calculations, inspired by the faint childhood memories of the Trachtenberg method of arithmetic manipulations, and achieving error rates of 1% or less.

The Centigrade temperature scale is more properly called Celsius, but the term Centigrade continues to be in more common use in many countries.

Kilos and pounds are easier to convert, here are the examples:

Easier Method for Temperature - Divide or Multiply by 2?
As to whether the above method for Centigrade-Fahrenheit conversions is easy - well, it is easier than multiplying by 5 and dividing by 9. On the other hand, this is more complex than just dividing by 2, which is another way to handle 5 divided by 9, but that results in a greater error, one that is perceivable when experiencing the cold weather in Montréal!

For Fahrenheit to Centigrade conversions, using 1/2 instead of 5/9 gives an error of 11%, which can be a lot since 86 °F becomes 27 °C instead of the actual 30 °C.

For Centigrade to Fahrenheit conversions, using 2 instead of 9/5 gives an error that increases in proportion to the size of the Centigrade value, getting to a maximum of 20%. This can be a problem, for example, when looking at the thermostat that is set at 18 °C. Using the double and add 32 method gives 68 °F, but the correct value is 64.4 °F, and this difference will be noticeable in getting to the right level of warmth in the room.